The working electrode in the flow channel of a flow-through electrolytic detection cell is preconditioned by flowing a preconditioning electroplating solution with preconditioner species through the flow channel while applying a negative potential. Flow of liquid through the flow channel is rapidly switched from preconditioning solution to a target solution containing an organic target solute to be measured. The transient response of the system resulting from exposure of the working electrode to organic target solute is detected by measuring current density during an initial transient time period. An unknown concentration of target solute is determined by comparing the transient response with one or more transient responses characteristic of known concentrations. A preferred measuring system is operable to switch flow from preconditioning solution to target solution in about 200 milliseconds or less.